This invention concerns a drill bit direct drive for deep well drilling tools.
With a known drill bit direct drive of this type (German Patent No. 3,513,124 U.S. equivalent 4,629,013), the bearing segments are each arranged on a free end of a flexible bar that is part of the bearing ring. Such an axial bearing design is especially low in wear, because development of a convergent gap relative to the bearing segments in the direction of rotation of the bearing ring is possible due to the tiltability of the bearing segments, and the oil well fluid can form a film of lubricant in this gap. The bending bars are also suitable for withstanding very high loads, but they have a very low eqaulization of tolerance to the axial bearing per trace ring/bearing ring pair. In cases in which a relatively great equalization of tolerance by the axial bearing is necessary, the axial bearing may have to have a number of trace ring/bearing ring pairs, which is in turn associated with a high cost and also with a substantial structural size of the axial bearing. If instead a favorable tolerance equalization is achieved by varying the spring characteristics and consequently the operating spring range, then the load bearing capacity of the axial bearing is reduced as is its lifetime, because the deflection angle becomes larger and thus the effective load transmitting friction contract face between the trace ring and the bearing segments becomes smaller.
This invention is based on the problem of creating a drill bit direct drive with an axial bearing that is suitable especially for very high axial loads and will yield a greater equalization of tolerance while maintaining the same load bearing conditions in the bearing as well as yielding favorable manufacturing conditions plus being easily adapted to different requirements.
The axial bearing of the drill bit direct drive according to this invention makes it possible for the bearing body to be shifted axially wiht a far greater operating spring range while maintaining the tiltability of the bearing body so a lubricant gap can be formed and thus the operating characteristics are favorable from the standpoint of wear, so the bearing yields a high equalization of tolerance. Its spring characteristic can be varied simply by means of the longitudinal and cross-sectional dimensions of the compression spring rod, so the axial bearing can easily be adapted to different requirements. At a high load bearing capacity of the axial bearing, the compression spring rods of the bearing segments assure an axial displacement independent of tilting displacement so there are no changes in load transmitting surfaces and thus the load conditions remain the same. Despite the relative length of the compression spring rods, the axial bearing according to this invention is compact in design, because as a rule the load bearing capacity adn the tolerance equalizing power of the axial bearing according to this invention eliminates the need for providing several trace ring/bearing ring pairs one after the other axially.
An especially elegant possibility of reducing the axial structural height is provided by a design whereby the compression spring rod is supported in a tension tubular spring which can in turn be supported again in a compression tubular spring in another version. This telescopic spring combination, so to speak, permits not only a reduction in the axial structural height of the bearing ring but also makes it possible to vary the spring characteristics of the support of the bearing body of the bearing segments, e.g., to achieve a greater spring range.